Reducing cardiac dose in post-operative irradiation of breast cancer patients: the relative importance of patient positioning and CT scan planning

Left-sided post-operative radiotherapy fields for the treatment of breast c ancer inevitably encompass the heart within the treatment volume, resulting in late mortality which may negate the cause-specific survival advantage o f the therapy. The effect of positioning was studied in 11 patients with le ft-sided tumours and live with right-sided rumours receiving routine postop erative radiotherapy to the breast or chest wall as part of primary therapy for breast cancer. Using the same arrangement of glancing fields for each patient treatment position, the optimum patient positioning resulted in a r eduction in cardiac dose compared to our standard patient treatment positio n. On the left side the reduction in mean cardiac dose was 60% (p<0.001) an d the reduction in maximum dose was 32% (p<0.001); on the right it was 17% and 31%, respectively. The volume of cardiac tissue irradiated was also red uced for all patients. Using this optimum treatment position, cardiac dose was investigated in a further 10 patients with left-sided tumours and our s tandard glancing field set-up was compared with 3-dimensional planning. A f urther reduction of 12% in the mean cardiac dose was achieved. 5 of 10 pati ents had a further small reduction of 4.6% in the maximum dose and one pati ent had a further reduction in maximum dose of 58%. In conclusion, sophisti cated radiotherapy planning can reduce cardiac doses, but optimum patient p ositioning is of greater importance. The general application of such relati vely simple measures could have a significant positive effect on overall su rvival from breast cancer.